This invention relates to color control apparatus for use in color video signal receiving apparatus and, more particularly, to such color control apparatus wherein many of the circuits normally provided for automatic chrominance (ACC) and/or automatic phase control (APC) also are used by VIR-responsive color saturation and/or hue control circuits.
A so-called vertical interval reference (VIR) signal is inserted into the nineteenth line interval of the vertical blanking interval in the color video signal which is broadcasted by many television broadcast stations. The purpose of this inserted VIR signal is to provide certain predetermined reference parameters, or characteristics, whereby video signal receiving apparatus, upon detecting these parameters or characteristics can effect an automatic color correction operation, whereby the ultimately reproduced color video picture exhibits proper color saturation and hue.
In the absence of a VIR signal, color saturation and hue characteristics of the reproduced video picture are controlled by the usual automatic chrominance control (ACC) and automatic phase (APC) circuits which are responsive to the level and phase, respectively, of the burst signal which is included in the received color video signal. Thus, the ACC circuit includes a gain-controlled amplifier for adjusting the level of the chrominance component included in the color video signal in accordance with the difference between the detected level of the burst signal and a predetermined reference level. Since the gain of the chrominance component determines the color saturation level, the ACC circuit functions to automatically control the color saturation characteristic. The APC circuit detects the phase differential between the burst signal and a locally generated oscillating signal which is used to demodulate the received chrominance component. This APC circuit functions to lock the phase of the local oscillating signal to the phase of the burst signal so as to properly establish the demodulating axis and automatically control the hue of the reproduced video picture. That is, it is assumed that the hue characteristic is correct when the phase of the local oscillating signal is locked to the phase of the burst signal.
While ACC and APC circuits generally are adequate in their respective operations, the level, or gain, of the chrominance component, as well as the phase of the chrominance subcarrier during the information portion of a horizontal line interval may differ from the corresponding gain and phase of the burst signal. Thus, ACC and APC circuits, by themselves, may not offer completely satisfactory results, especially with respect to the flesh tone colors of the reproduced video picture. For these reasons, the insertion of the VIR signal into the vertical blanking interval, and the use of color control circuits which are responsive to this VIR signal have been adopted.
The VIR signal which now is used in the industry is formed of a reference subcarrier, equal in frequency and phase to the usual burst signal, this reference subcarrier being superposed on a predetermined reference luminance level and being transmitted during a preselected chrominance reference portion of the VIR signal. This is designated herein as the chrominance reference signal. Following this chrominance reference signal, the VIR signal is provided with a luminance reference signal of predetermined amplitude and duration. A black reference signal of a respectively predetermined amplitude and duration then follows the luminance reference signal. As in the transmission of a normal line interval, the VIR signal also includes horizontal synchronizing pulses and a burst signal. When the VIR signal is received, the reference information provided by the chrominance reference signal, the luminance reference signal and the black reference signal is used to control the gain, or level, of the chrominance channel, thereby controlling the color saturation, and the phase of the locally generated oscillating signal used for demodulation, thereby controlling the hue characteristic.
In a typical VIR-controlled color correction circuit, the level of one of the demodulated color difference signals which is produced in response to the chrominance reference signal included in the VIR signal is detected. The level of this demodulated color difference signal should, of course, correspond to a predetermined level for proper color saturation chracteristics. Thus, any difference between the actual level and the predetermined level is used to vary the gain of the chrominance channel. Typically, a high gain amplifier is used for such gain adjustments. Similarly, the level of another demodulated color difference signal is detected during the time that the chrominance reference signal of the VIR signal is received. For correct hue characteristics, it is expected that this demodulated color difference signal will have a predetermined level. In the event that the actual level differs from the expected predetermined level, this difference is used to vary the phase of the local oscillating signal which is utilized for color demodulation. Typically, a high gain amplifier is relied upon for this phase control.
Typical of this type of VIR-controlled color correction is the apparatus disclosed in U.S. Pat. No. 3,950,780, issued Apr. 13, 1976. An improved VIR-controlled color correction circuit is disclosed in our copending application Ser. No. 839,847, filed Oct. 6, 1977. Yet another example of such VIR-controlled color correction circuitry is disclosed in our copending application Ser. No. 825,186, filed Aug. 16, 1977. In color video signal receiving apparatus which includes such circuitry, such as in a color television receiver or a video signal recorder/reproducer (for example a VTR device), it is necessary that the usual ACC and APC circuitry also be provided. Typically, the ACC circuit is separate and apart from the VIR-controlled color saturation control circuit; and the APC circuit likewise is separate and apart from the VIR-controlled hue correction circuit. By providing such independent circuits, there is a duplication in many circuit components which perform analogous functions but in different control circuits. Heretofore, individual high gain amplifiers have been provided in the ACC circuit, the VIR-controlled color saturation correction circuit, the APC circuit and the VIR-controlled hue correction circuit. Such high gain amplifiers are relatively expensive, and the respective circuits in which they are used are relatively complex, primarily because of redundancy. Consequently, the overall cost of production for such color video signal receiving apparatus is high.